Blends of Polyhydroxyalkanoates (PHAs) - Polyhydroxyalkanoate (PHA) Based Blends, Composites and Nanocomposites - page 88

mechanical properties. Good mechanical properties of P(3HB)/starch blends
were observed at low concentrations of starch up to 10 wt%. However, a
further increase of starch content decreased the stiffness of the blends due
to weak adhesion between the P(3HB) matrix and starch particles. P(3HB)/
starch: 90/10 wt% possessed a good combination of stiffness, strength, and
toughness. The SEM micrograph of this blend showed relatively good dis-
persion and interfacial adhesion between starch granules and the P(3HB)
matrix. The starch granules were also shown to be embedded in the P(3HB)
matrix even after the rupture process. 47
The biodegradation of the P(3HB)/starch blend was determined based
on the weight loss measurement through utilization of P(3HB) and its
blend by actinomycetes. The results indicated that the higher the starch
content, the faster the rate of biodegradation. Degradation of the P(3HB)/
starch blend was also affected significantly when the blends containing
medium were supplemented with different carbon and nitrogen sources.
A lower degradation of blend was observed for the medium supplemented
with peptone, ammonium chloride and ammonium oxalate while an in-
crease in the degradation was observed when calcium nitrate, potassium
nitrate or ammonium molybdate were supplemented in the medium.
The optimum conditions for the biodegradation of the P(3HB)/starch
blend was at a pH of 7, temperature of 30 1C and medium supplemented
with glucose or calcium acetate as carbon and nitrogen sources,
respectively. 47
The properties of P(3HB) when blended with two types of maize starch,
Starch 1 (containing 70% amylose) and Starch 2 (containing 72% amylo-
pectin) was examined by Zhang et al. 45 The SEM micrographs showed that
starch acted as a filler for the P(3HB)/starch blend. The occurrence of
intermolecular hydrogen bonding between P(3HB) and both types of maize
starch was detected using FT-IR. In addition, the WAXD results revealed that
the addition of starch affected the crystal structure of P(3HB). Starch 1 has
stronger intermolecular hydrogen bonding with P(3HB) compared to Starch
2 due to its high-amylose content and linear structure. The existence of
hydrogen bonding between the hydroxyl groups of starch and carbonyl
groups of P(3HB) might inhibit chain scission degradation in P(3HB), which
led to the improvement of the thermal stability, melt viscosity, and mech-
anical properties of the P(3HB)/starch blends. Higher melt shear viscosity,
better mechanical properties and stability were observed for the blend
containing Starch 1 compared to Starch 2 due to the stronger hydrogen
bonding effect between P(3HB) and Starch 1.
Ramsay et al. 48 reported that addition of 50 wt% starch to P(3HB-co-3HV)
copolymer resulted in a material that exhibited useful thermoplastic prop-
erties. The elongation at break increased as the amount of starch added
decreased. The same trend was observed for Young's modulus. It was also
reported that starch with altered surface properties would adhere more
strongly to P(3HB-co-3HV) copolymer,

d n 2 r 4 n g | 6

.

thus increasing the strength of

the blend.